Nearly a tie: Australia and Brazil differ by barely -9%% in area — about 7,706,009 km² km² against 8,499,400 km² km².
Australia sits in Oceania, Brazil in South America. On the old Mercator map the latitude gap distorted how large each felt beside the other; at true size the answer is simply 0.9×.
The old Mercator map treated both about equally (1.2× vs 1× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Brazil fits 0× into Australia.